Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes a field effect transistor (FET). The FET includes a first channel, a first source and a first drain; a second channel, a second source and a second drain; and a gate structure disposed over the first and second channels. The gate structure includes a gate dielectric layer and a gate electrode layer. The first source includes a first crystal semiconductor layer and the second source includes a second crystal semiconductor layer. The first source and the second source are connected by an alloy layer made of one or more Group IV element and one or more transition metal elements. The first crystal semiconductor layer is not in direct contact with the second crystal semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 16/228,872, filed Dec. 21, 2018, which is aContinuation Application of U.S. patent application Ser. No. 15/418,995filed Jan. 30, 2017, which claims priority to U.S. Provisional PatentApplication 62/427,597 filed Nov. 29, 2016, the entire disclosures ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to semiconductor devices, such as integratedcircuits, and more particularly to semiconductor devices having silicidelayers formed on source/drain (S/D) structures and their manufacturingprocesses.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (Fin FET) and the use of a metal gate structurewith a high-k (dielectric constant) material. The metal gate structureis often manufactured by using gate replacement technologies, andsources and drains are formed by using an epitaxial growth method.Source/drain contact plugs are also formed on the sources/drains, ofwhich contact resistance should be low.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A-1D show exemplary cross sectional views of various stages formanufacturing a semiconductor device according to some embodiments ofthe present disclosure.

FIGS. 2A-2B show exemplary cross sectional views and FIGS. 2C-2D showexemplary perspective views of various stages for manufacturing asemiconductor device according to some embodiments of the presentdisclosure.

FIGS. 3A-3D show exemplary perspective views of various stages formanufacturing a semiconductor device according to some embodiments ofthe present disclosure.

FIGS. 4A-4C show exemplary perspective views of various stages formanufacturing a semiconductor device according to some embodiments ofthe present disclosure.

FIGS. 5A-5D show exemplary perspective views of various stages formanufacturing a semiconductor device according to another embodiment ofthe present disclosure.

FIGS. 6A-6C show exemplary perspective views of various stages formanufacturing a semiconductor device according to another embodiment ofthe present disclosure.

FIG. 7 is an exemplary cross sectional view of source/drain structuresof a fin field effect transistor (FinFET) according to some embodimentsof the present disclosure.

FIG. 8 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 9 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 10 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 11 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 12 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 13 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIG. 14 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.

FIGS. 15A-15D show exemplary cross sectional views of various stages formanufacturing a semiconductor device according to another embodiment ofthe present disclosure.

FIGS. 16A-16B show exemplary cross sectional views and FIGS. 16C-16Dshow exemplary perspective views of various stages for manufacturing asemiconductor device according to some embodiments of the presentdisclosure.

FIGS. 17A-17D show exemplary perspective views of various stages formanufacturing a semiconductor device according to another embodiment ofthe present disclosure.

FIGS. 18A-18C show exemplary perspective views of various stages formanufacturing a semiconductor device according to another embodiment ofthe present disclosure.

FIG. 19 is an exemplary cross sectional view of source/drain structuresof a gate-all-around field effect transistor (GAA FET) according to someembodiments of the present disclosure.

FIG. 20 shows exemplary cross sectional views of source/drain structuresof a gate-all-around field effect transistor (GAA FET) according to someembodiments of the present disclosure.

FIGS. 21A and 21B are exemplary cross sectional views of source/drainstructures of a gate-all-around field effect transistor (GAA FET)according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanied drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” Further, inthe following fabrication process, there may be one or more additionaloperations in/between the described operations, and the order ofoperations may be changed.

FIGS. 1A-4C show exemplary cross sectional views of various stages formanufacturing a FinFET according to some embodiments of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 1A-4C, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable.

In the manufacturing method for a FinFET, fin structures are formed. Amask layer 10 is formed over a substrate 50, as shown in FIG. 1A. Themask layer 10 is formed by, for example, a thermal oxidation processand/or a chemical vapor deposition (CVD) process. The substrate 50 is,for example, a p-type silicon substrate with an impurity concentrationin a range from about 1×10¹⁵ cm⁻³ to about 1×10¹⁶ cm⁻³. In otherembodiments, the substrate is an n-type silicon or germanium substratewith an impurity concentration in a range from about 1×10¹⁵ cm⁻³ toabout 1×10¹⁶ cm⁻³.

Alternatively, the substrate 50 may comprise another elementarysemiconductor, such as germanium; a compound semiconductor includingGroup IV-IV compound semiconductors such as SiC and SiGe, Group III-Vcompound semiconductors such as GaAs, GaP, GaN, InP, InAs, InSb, GaAsP,AlGaN, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinationsthereof. The substrate 50 may include various regions that have beensuitably doped with impurities (e.g., p-type or n-type conductivity).

The mask layer 10 includes, for example, a pad oxide (e.g., siliconoxide) layer 11 and a silicon nitride mask layer 12, as shown in FIG.1A, in some embodiments.

The pad oxide layer 11 may be formed by using thermal oxidation or a CVDprocess. The silicon nitride mask layer 12 may be formed by a physicalvapor deposition (PVD), such as a sputtering method, a CVD,plasma-enhanced chemical vapor deposition (PECVD), an atmosphericpressure chemical vapor deposition (APCVD), a low-pressure CVD (LPCVD),a high density plasma CVD (HDPCVD), an atomic layer deposition (ALD),and/or other processes.

The thickness of the pad oxide layer 11 is in a range from about 2 nm toabout 15 nm and the thickness of the silicon nitride mask layer 12 is ina range from about 2 nm to about 50 nm in some embodiments.

A mask pattern is further formed over the mask layer. The mask patternis, for example, a resist pattern formed by lithography operations. Byusing the mask pattern as an etching mask, a hard mask pattern of thepad oxide layer 11 and the silicon nitride mask layer 12 is formed, asshown in FIG. 1B.

Then, as shown in FIG. 1C, by using the hard mask pattern as an etchingmask, the substrate 50 is patterned into fin structures 52 for an n-typeFET and fin structures 54 for a p-type FET by trench etching using a dryetching method and/or a wet etching method. The dimensions for the finstructures 52 for an n-type FET may be the same as or different fromthose for the fin structures 54 for a p-type FET.

In FIG. 1C, two fin structures 52 and two fin structures 54 are disposedover the substrate 50. However, the number of the fin structures is notlimited to two. The numbers may be as small as one or more than three.In addition, one or more dummy fin structures may be disposed adjacentboth sides of the fin structures 52 and/or the fin structures 54 toimprove pattern fidelity in patterning processes.

The fin structures 52, 54 may be made of the same material as thesubstrate 50 and may continuously extend or protrude from the substrate50. In this embodiment, the fin structures are made of Si. The siliconlayers of the fin structures 52, 54 may be intrinsic, or appropriatelydoped with an n-type impurity or a p-type impurity.

The width W1 of the fin structures 52, 54 is in a range from about 5 nmto about 40 nm in some embodiments, and is in a range from about 7 nm toabout 12 nm in other embodiments. The space Si between two finstructures is in a range from about 10 nm to about 40 nm in someembodiments. The height H1 (along the Z direction) of the fin structures52, 54 is in a range from about 100 nm to about 300 nm in someembodiments, and is in a range from about 50 nm to 100 nm in otherembodiments.

The lower part of the fin structures 52, 54 may be referred to as a wellregion, and the upper part of the fin structures 52, 54, which iscovered by a gate electrode may be referred to as a channel or a channelregion, and the upper part of the fin structures 52, 54, which is notcovered by the gate electrode may be referred to as a source and adrain, or a source region and a drain region. In this disclosure,“source” and “drain” may be collectively referred to as “source/drain.”The height of the well region is in a range from about 60 nm to 100 nmin some embodiments, and the height of the channel region is in a rangefrom about 40 nm to 120 nm, and is in a range from about 38 nm to about60 nm in other embodiments.

After the fin structures 52, 54 are formed, a first protective layer 15is formed to cover the structures 52, 54, as shown in FIG. 1D. The firstprotective layer 15 is made of, for example, silicon oxide, siliconnitride (SiN) or silicon oxynitride (SiON). In an embodiment, the firstprotective layer 15 is made of SiN. The first protective layer 15 can beformed by CVD. The thickness of the first protective layer 15 is in arange from about 1 nm to about 20 nm in some embodiments.

After the first protective layer 15 is formed, a second protective layer17 is formed as shown in FIG. 2A. The second protective layer 17 is madeof, for example, silicon oxide, silicon nitride (SiN) or siliconoxynitride (SiON) and is different from the first protective layer 15.In an embodiment, the second protective layer 15 is made of siliconoxide. The second protective layer 17 can be formed by CVD. Thethickness of the second protective layer 17 is in a range from about 1nm to about 20 nm in some embodiments.

Further, an isolation insulating layer 58 is formed in spaces betweenthe fin structures and/or a space between one fin structure and anotherelement formed over the substrate 50, as shown in FIG. 2B. The isolationinsulating layer 58 may also be called a “shallow-trench-isolation(STI)” layer. The insulating material for the isolation insulating layer58 may include one or more layers of silicon oxide, silicon nitride,silicon oxynitride (SiON), SiOCN, fluorine-doped silicate glass (FSG),or a low-k dielectric material. The isolation insulating layer is formedby LPCVD (low pressure chemical vapor deposition), plasma-CVD orflowable CVD. In the flowable CVD, flowable dielectric materials insteadof silicon oxide may be deposited. Flowable dielectric materials, astheir name suggest, can “flow” during deposition to fill gaps or spaceswith a high aspect ratio. Usually, various chemistries are added tosilicon-containing precursors to allow the deposited film to flow. Insome embodiments, nitrogen hydride bonds are added. Examples of flowabledielectric precursors, particularly flowable silicon oxide precursors,include a silicate, a siloxane, a methyl silsesquioxane (MSQ), ahydrogen silsesquioxane (HSQ), an MSQ/HSQ, a perhydrosilazane (TCPS), aperhydro-polysilazane (PSZ), a tetraethyl orthosilicate (TEOS), or asilyl-amine, such as trisilylamine (TSA). These flowable silicon oxidematerials are formed in a multiple-operation process. After the flowablefilm is deposited, it is cured and then annealed to remove un-desiredelement(s) to form silicon oxide. When the un-desired element(s) isremoved, the flowable film densifies and shrinks. In some embodiments,multiple anneal processes are conducted. The flowable film is cured andannealed more than once. The flowable film may be doped with boronand/or phosphorous.

The insulating layer 58 is first formed in a thick layer as shown inFIG. 2B so that the fin structures are embedded in the thick layer, andthe thick layer is recessed so as to expose the upper portions of thefin structures 52, 54, as shown in FIG. 2C. The insulating layer 58 canbe recessed by using dry and/or wet etching. In some embodiments, themask layers 11 and 12 and the first and second protective layers 15 and17 are also removed from the exposed portions of the structures 52, 54.

The height H2 of the fin structures from the upper surface of theisolation insulating layer 58 is in a range from about 20 nm to about100 nm in some embodiments, and is in a range from about 30 nm to about50 nm in other embodiments. After or before recessing the isolationinsulating layer 58, a thermal process, for example, an anneal process,may be performed to improve the quality of the isolation insulatinglayer 58. In certain embodiments, the thermal process is performed byusing rapid thermal annealing (RTA) at a temperature in a range fromabout 900° C. to about 1050° C. for about 1.5 seconds to about 10seconds in an inert gas ambient, such as an N₂, Ar or He ambient.

In some embodiments, a gate replacement technology is employed. Afterthe insulating layer 58 is formed (and recessed), a dummy gate structureincluding a dummy gate dielectric layer 20 and a dummy gate electrodelayer 22 is formed over the fin structures 52, 54, as shown in FIG. 2D.As shown in FIG. 2D, the gate structure extends in the X direction,while the fin structures extend in the Y direction.

To fabricate the dummy gate structure, a dielectric layer and a polysilicon layer are formed over the isolation insulating layer 58 and theexposed fin structures 52, 54, and then patterning operations areperformed so as to obtain the dummy gate structure including a dummygate electrode layer 22 made of poly silicon and a dummy gate dielectriclayer 20. In some embodiments, the polysilicon layer is patterned byusing a hard mask and the hard mask remains on the dummy gate electrodelayer 22 as a cap insulating layer. The hard mask (cap insulating layer)includes one or more layers of insulating material. The cap insulatinglayer includes a silicon nitride layer formed over a silicon oxide layerin some embodiments. In other embodiments, the cap insulating layerincludes a silicon oxide layer formed over a silicon nitride layer. Theinsulating material for the cap insulating layer may be formed by CVD,PVD, ALD, e-beam evaporation, or other suitable process. In someembodiments, the dummy gate dielectric layer 20 may include one or morelayers of silicon oxide, silicon nitride, silicon oxy-nitride, or high-kdielectrics. In some embodiments, a thickness of the dummy gatedielectric layer 20 is in a range from about 2 nm to about 20 nm, and ina range from about 2 nm to about 10 nm in other embodiments. The heightof the dummy gate structures is in a range from about 50 nm to about 400nm in some embodiments, and is in a range from about 100 nm to 200 nm inother embodiments.

If a gate-first technology is employed, the dummy gate electrode layer22 and the dummy gate dielectric layer 20 are used as a gate electrodeand a gate dielectric layer.

Further, sidewall spacers 24 are formed on opposite sidewalls of thedummy gate electrode layer 22, as shown in FIG. 3A. The sidewall spacers24 include one or more layers of insulating material, such as SiO₂, SiN,SiON, SiOCN or SiCN, which are formed by CVD, PVD, ALD, e-beamevaporation, or other suitable process. A low-k dielectric material maybe used as the sidewall spacers. The sidewall spacers 24 are formed byforming a blanket layer of insulating material and performinganisotropic etching. In an embodiment, the sidewall spacer layers aremade of silicon nitride based material, such as SiN, SiON, SiOCN orSiCN. The thickness of the sidewall spacers 24 is in a range from about2 nm to about 10 nm in some embodiments.

Then, as shown in FIG. 3B, the sidewall spacers 24 formed on the finstructures 52, 54 are removed by using, for example, anisotropic dryetching, so as to expose source/drain regions of the structures 52, 54.

After the source/drain regions of the structures 52, 54 are exposed,source/drain epitaxial layers are formed, as shown in FIG. 3C. Thesource/drain epitaxial layer 60 for the n-type FET includes one or morelayers of semiconductor material, such as, SiC, SiP and SiCP, whichprovides appropriate stress to the channel of the n-type FET, in someembodiments. When SiP or SiCP is used as multi epitaxial layers, thelayers have different P and/or C concentrations. Since the fin structure52 is a crystalline Si, the epitaxial layer 60 is also crystalline. Thesource/drain epitaxial layer 62 for the p-type FET includes one or moreof a semiconductor material, such as, Ge and Si_(x)Ge_(1-x) where 0<x<1,which provides appropriate stress to the channel of the p-type FET, insome embodiments. When SiGe is used as the multi epitaxial layers, thelayers have different Ge concentrations. Since the fin structures 52, 54are crystalline Si, the epitaxial layers 60, 62 are also crystalline. Incertain embodiments, a Group III-V material which provides appropriatestress to the channel is used as the source/drain epitaxial layers 60and/or 62. In some embodiments, the source/drain epitaxial layers 60and/or 62 include multiple layers of epitaxially formed semiconductormaterials.

The source/drain epitaxial layers 60, 62 may be grown at a temperatureof about 400 to 800° C. under a pressure of about 80 to 150 Torr, byusing a Si containing gas such as SiH₄, Si₂H₆ or SiCl₂H₂; a Gecontaining gas, such as GeH₄, Ge₂H₆ or GeCl₂H₂; a C containing gas, suchas CH₄ or C₂H₆; and/or a dopant gas, such as PH₃. The source/drainstructure for an n-type FET and the source/drain structure for a p-typeFET may be formed by separate epitaxial processes.

In the present disclosure, after the source/drain epitaxial layers 60,62 are formed, the source/drain epitaxial layer 60 formed on one finstructure 52 is not in contact with (i.e., physically separated from)the source/drain epitaxial layer 60 formed on the adjacent fin structure52 as shown in FIG. 3C. Similarly, the source/drain epitaxial layer 62formed on one fin structure 54 is not in contact with (i.e., physicallyseparated from) the source/drain epitaxial layer 62 formed on theadjacent fin structure 54 as shown in FIG. 3C. The space S2 between thesource/drain epitaxial layers 60 (or 62) is in a range from about 5 nmto 15 nm in some embodiments. The thicknesses of the source/drainepitaxial layers 60 and 62 are adjusted to secure the desired space S2depending on the space 51 (see, FIG. 1C) between two fin structures.

After the source/drain epitaxial layers 60 and 62 are formed, adielectric cover layer 65 is formed over the source/drain epitaxiallayers 60 and 62 and a first interlayer dielectric (ILD) layer 67 isformed over the dielectric cover layer 65, as shown in FIG. 3D. Thedielectric cover layer 65 is made of, for example, SiN or SiON, and hasa thickness in a range from about 2 nm to about 20 nm in someembodiments. The first ILD 67 is made of a different material than thedielectric cover layer 65 and is made of, for example, one or morelayers of silicon oxide, SiCN, SiOCN or a low-k material.

After the ILD layer 67 is formed, a metal gate structure is formed. Thedummy gate structures (the dummy gate electrode layer 22 and the dummygate dielectric layer 20) are removed and replaced with a metal gatestructures. In certain embodiments, the first ILD layer 67 is formedover the dummy gate structures and a planarization operation, such as achemical mechanical polishing (CMP) process or an etch-back process, isperformed to expose the upper surface of the dummy gate electrode layer22. Then, the dummy gate electrode layer 22 and the dummy gatedielectric layer 20 are removed, by appropriate etching processes,respectively, to form a gate opening. A metal gate structure including agate dielectric layer 72 and a metal gate electrode layer 74 are formedin the gate openings, as shown in FIG. 4A.

The gate dielectric layer 72 may be formed over an interface layer (notshown) disposed over the channel layer of the fin structures 52, 54. Theinterface layer may include silicon oxide or germanium oxide with athickness of 0.2 nm to 1.5 nm in some embodiments. In other embodiments,the thickness of the interface layer is in a range about 0.5 nm to about1.0 nm.

The gate dielectric layer 72 includes one or more layers of dielectricmaterials, such as silicon oxide, silicon nitride, or high-k dielectricmaterial, other suitable dielectric material, and/or combinationsthereof. Examples of high-k dielectric material include HfO₂, HfSiO,HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminum oxide, titaniumoxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-kdielectric materials, and/or combinations thereof. The gate dielectriclayer is formed by, for example, chemical vapor deposition (CVD),physical vapor deposition (PVD), atomic layer deposition (ALD), highdensity plasma CVD (HDPCVD), or other suitable methods, and/orcombinations thereof. The thickness of the gate dielectric layer is in arange from about 1 nm to about 10 nm in some embodiments, and may be ina range from about 2 nm to about 7 nm in other embodiments.

The metal gate electrode layer 74 is formed over the gate dielectriclayer. The metal gate electrode includes one or more layers of anysuitable metal material, such as aluminum, copper, titanium, tantalum,cobalt, molybdenum, tantalum nitride, nickel silicide, cobalt silicide,TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloys, other suitablematerials, and/or combinations thereof.

In certain embodiments, one or more work function adjustment layer 73 isinterposed between the gate dielectric layer 72 and the metal gateelectrode layer 74, as shown in FIG. 4A. The work function adjustmentlayer 73 is made of a conductive material such as a single layer of TiN,TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC, or amultilayer of two or more of these materials. For the n-channel Fin FET,one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSi and TaSi isused as the work function adjustment layer, and for the p-channel FinFET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC and Co is usedas the work function adjustment layer.

After depositing appropriate materials for the metal gate structure,planarization operations, such as CMP, are performed. Further, in someembodiments, the metal gate structure is recessed to form a cap space,and the cap space is filled with an insulating material 78, as shown inFIG. 4A.

After the metal gate structure is formed, the first ILD layer 67 anddielectric cover layer 65 are removed. In an embodiment, the first ILDlayer 67 and dielectric cover layer 65 are fully removed and in otherembodiments, the first ILD layer 67 and dielectric cover layer 65 arepartially removed from an area around the source/drain structures.

After the first ILD layer 67 is at least partially removed, a metalalloy layer 80, 81 is formed over the source/drain epitaxial layer 60and 62, as shown in FIG. 4B.

The metal alloy layer 80, 81 is an alloy made of one or more Group IVelement and one or more transition metal elements. When the source/drainepitaxial layer 60 and 62 are formed by silicon, the metal alloy layer80, 81 is a silicide layer. When the source/drain epitaxial layer 60 and62 are formed by germanium, the metal alloy layer 80, 81 is a germanidelayer. When the source/drain epitaxial layer 60 and 62 are formed bySiGe, the metal alloy layer 80, 81 is a silicide-germanide layer.

The transition metal includes one or more of Ti, Ta, Ni and Co. Thealloy layer 80, 81 is one or more of TiSi, TaSi, NiSi, CoSi, TiSiGe,TaSiGe, NiSiGe and CoSiGe.

After the first ILD layer 67 is removed, transition metal is depositedby, for example, CVD, ALD or PVD, on the source/drain epitaxial layer 60and 62. During the deposition, the deposited transition metal reactswith Si and/or Ge in the source/drain epitaxial layer 60 and 62, therebyforming the alloy layer 80, 81 in some embodiments. In some embodiments,silicide (alloy) layer can be formed by PECVD, CVD, PEALD, or ALD metaldeposit in a temperature range of about 250 to about 700° C., and thenan in-situ dry etching using Cl or F based gas or ex-situ wet selectiveetching is applied to remove the remaining metal on spacer and theisolation insulating layer. In other embodiments, the silicide (alloy)layer can be formed by PECVD, CVD, PEALD, or ALD metal deposit in atemperature range of about 350 to about 650° C. In certain embodiments,a nitridation treatment is later performed to passivate silicide surfacefor the subsequent silicide formation anneal. In other embodiments, aselective silicide deposition process through surface blocking byself-assembly molecular (SAMs), or inherent selective formation fromproper metal and silicon precursors is performed. Other suitablesilicide formation processes may be utilized.

In the present embodiments, before the alloy layer 80 is formed, thesource/drain epitaxial layer 60 of one of the fin structures isseparated from the source/drain epitaxial layer 60 of the adjacent finstructure, and the source/drain epitaxial layer 62 of one of the finstructures is separated from the source/drain epitaxial layer 62 of theadjacent fin structure. The alloy layer 80, 81 is formed such that theformed alloy layer 80 connects the source/drain epitaxial layer 60 ofone of the fin structures (52) and the source/drain epitaxial layer 60of the adjacent fin structure (52), and the formed alloy layer 81connects the source/drain epitaxial layer 62 of one of the finstructures (54) and the source/drain epitaxial layer 62 of the adjacentfin structure (54).

In some embodiments, after a transition metal layer is formed on thesource/drain epitaxial layer 60 and 62, an annealing operation isperformed to form the alloy layer 80. The annealing operation isperformed at a temperature of about 250° C. to about 850° C.

After the alloy layer 80, 81 is formed, a contact-etch stop layer (CESL)150 is formed to cover the alloy layer 80, 81, and a second ILD layer160 is formed on the CESL 150, as shown in FIG. 4C. The CESL 150 is madeof a silicon nitride based material, such as SiN and SiON, and has athickness in a range from about 2 nm to about 20 nm in some embodiments.The second ILD 160 is made of a different material than the CESL 150 andis made of, for example, one or more layers of silicon oxide, SiCN,SiOCN or a low-k material.

Subsequently, a patterning operation is performed to form contactopenings over the alloy layer 80, 81 of the source/drain structure, andthe openings are filled with a conductive material, thereby formingcontact plugs 200 and 201, as shown in FIG. 4C. The contact plugs 200and 201 include a single layer or multiple layers of any suitable metalsuch as Co, W, Ti, Ta, Cu, Al and/or Ni and/or nitride of Ti or Ta.

After forming the contact plugs, further CMOS processes are performed toform various features such as one or more additional interlayerdielectric layers, contacts/vias, interconnect metal layers, andpassivation layers, etc.

Although in the foregoing embodiments and the following embodiments, ann-channel FET and a p-channel FET are illustrated adjacent to eachother, the arrangement of the n-channel FET and the p-channel FET is notlimited to such an arrangement.

FIGS. 5A-6C show exemplary cross sectional views of various stages formanufacturing a FinFET according to another embodiment of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 5A-6C, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. The same or similarconfigurations, materials, processes and/or operation as described withFIG. 1A-4C may be employed in the following embodiments, and thedetailed explanation may be omitted.

After the structure as shown in FIG. 3D is formed, the first ILD 67 isrecessed by dry and/or wet etching so as to the top portions of thesource/drain epitaxial layers 60 and 62 are exposed, as shown in FIG.5A.

Then, as shown in FIG. 5B, the source/drain epitaxial layers 60 and 62and the fin structures 52 are removed by dry and/or wet etching so as toform openings 111 and 112. The fin structures 52 are recessed to thelevel of the upper surface of the isolation insulating layer 58. In someembodiments, the fin structures 52 are recessed below the upper surfaceof the isolation insulating layer 58. After the openings 111, 112 areformed, a source/drain epitaxial layer 113 for an n-channel FET and asource/drain epitaxial layer 114 for a p-channel FET are formed, asshown in FIG. 5C.

In some embodiments, after the first ILD layer 67 is recessed, one ofthe n-channel FET region and the p-channel FET region is covered by aprotective layer (e.g., SiN) and the operations as explained with FIGS.5B and 5C are performed separately for the n-channel FET region and thep-channel FET region, respectively.

The source/drain epitaxial layer 113 for the n-channel FET includes oneor more layers of Si, SiC, SiP and SiCP, and the source/drain epitaxiallayer 114 for the p-channel FET includes one or more layers of Ge andSi_(x)Ge_(1-x) where 0<x<1.

Subsequently, an ILD layer 117 is formed over the source/drain epitaxiallayers 113 and 114 and the first ILD layer 67, as shown in FIG. 5D. TheILD layer 117 is made of the same or similar material as the first ILDlayer 67.

Then, the same or similar operations as described with FIG. 4A areperformed and a metal gate structure including a gate dielectric layer72 and a metal gate electrode layer 74 are formed, as shown in FIG. 6A.Further, the same or similar operations as described with FIG. 4B areperformed, an alloy layer 80, 81 are formed so as to connect twoadjacent source/drain epitaxial layers, as shown in FIG. 6B.Subsequently, he same or similar operations as described with FIG. 4Care performed, contact plugs 200 and 201 are formed, as shown in FIG.6C. After forming the contact plugs, further CMOS processes areperformed to form various features such as additional interlayerdielectric layer, contacts/vias, interconnect metal layers, andpassivation layers, etc.

FIGS. 7-14 are exemplary cross sectional views of source/drainstructures of a fin field effect transistor (FinFET) according tovarious embodiments of the present disclosure. In FIGS. 7-14, ann-channel FET (NFET) and a p-channel FET (PFET), each of which includestwo fin structures 52, 54 are illustrated as adjacent to each other.However, the configuration is not limited to this. The number of the finstructures may be three or more and one or more additional structuresmay be disposed between the NFET and the PFET.

In FIG. 7, in the n-channel FET (NFET), a first n-type epitaxial layer132 is formed on the fin structure 52, and a second n-type epitaxiallayer 134 is formed on the first n-type epitaxial layer 132. The firstand second n-type epitaxial layers are crystalline semiconductor layers,such as Si, SiC, SiCP, SiP, Ge and SiGe, having different latticeconstants from each other and from the fin structure. When SiC, SiPand/or SiCP are used, the C or P concentration of the second n-typeepitaxial layer 134 is higher than that of the first n-type epitaxiallayer 132. In some embodiments, a Group III-V semiconductor layer isused for at least one of the first and second n-type epitaxial layers.The combination of the first and second n-type epitaxial layers 132 and134 correspond to the source/drain epitaxial layer 60. In otherembodiments, only one of the first and second n-type epitaxial layers132 and 134 is formed, and in certain embodiments, three or more n-typeepitaxial layers are formed.

Further, the alloy layer 222, for example, a silicide layer, whichcorresponds to the alloy layer 80, is formed on the second n-typeepitaxial layer 134. The alloy layer 222 is formed by a reaction betweenthe material of the second n-type epitaxial layer 134 and a transitionmetal layer formed thereon. As shown in FIG. 7, the second n-typeepitaxial layer 134 of one of the adjacent two fin structure 52 does nottouch the second n-type epitaxial layer 134 of the other one of theadjacent two fin structure 52. The alloy layer 222 fills the spacebetween two second n-type epitaxial layers 134 and physically andelectrically connects the two second n-type epitaxial layers 134.

In some embodiments, a residual transition metal 215, which has notfully reacted with the second n-type epitaxial layer 134 remain. In sucha case, the remaining transition metal can be converted to a passivationlayer by a subsequent nitridation operation by using NH₃ or N₂+H₂ plasmain some embodiments. The passivation layer covers the surface of thealloy layer 222 to protect the alloy layer 222 from damages caused bythe subsequent processes. Further, a CESL 150 covers the n-typesource/drain structure, as shown in FIG.7.

The contact plug 200 is in contact with the alloy layer 222. In someembodiments, the contact plug 200 includes a barrier layer 202 made of,for example, TiN or TaN, and a body layer 210 made of, for example, Co,W, Ti, Ta, Cu, Ru, Rh, Jr, Al and/or Ni.

In FIG. 7, a transition metal layer 225 remains at the bottom of thevoid 224 formed by the alloy layer 222 and the isolation insulatinglayer 58. The volume of the transition metal layer 225 is sufficientlysmall so as not to affect electrical properties of the NFET.

Further, in FIG. 7, spacer residues 110, which are a remaining part ofthe sidewall spacers 24 that is not etched in the operation of FIG. 3B,exist.

The width T11 (the largest width) of the fin structure 52 surrounded bythe first n-type epitaxial layer along the X direction is in a rangefrom about 4 nm to about 10 nm in some embodiments. The thickness T12 ofthe first n-type epitaxial layer 132 is in a range from about 0.5 nm toabout 3 nm in some embodiments, and the thickness T13 of the secondn-type epitaxial layer 134 is in a range from about 2 nm to about 8 nmin some embodiments. The space T15 between the two adjacent secondn-type epitaxial layers 134 is in a range from about 0.5 nm to about 20nm in some embodiments. In some embodiments, the isolation insulatinglayer 58 is etched in the operation of FIG. 3B, and the etched amountH11 is in a range from about 0.5 nm to about 20 nm. The verticalthickness of the spacer residue 110 is in a range from about 0.5 nm toabout 30 nm in some embodiments.

In some embodiments, one or more voids 143 are formed during the alloylayer formation. The shapes of the voids 143 in the cross section mayinclude a rhombus, a circle, an oval or an irregular shape. The shapesmay be symmetry or asymmetric. The number of the voids may be as smallas one in some embodiments, and more than one in other embodiments.Sizes of the multiple voids and spaces between voids may besubstantially the same or different.

The p-channel FET (PFET) shown in FIG. 7 has the same or similarstructure as the n-channel FET (NFET), and explanations for the commonconfigurations may be omitted. A first p-type epitaxial layer 136 isformed on the fin structure 54, and a second p-type epitaxial layer 138is formed on the first p-type epitaxial layer 136. The first and secondp-type epitaxial layers are crystalline semiconductor layers, such asSi, SiC, SiCP, SiP, Ge and SiGe, having different lattice constants fromeach other and from the fin structure. When SiGe is used, the Geconcentration of the second p-type epitaxial layer 138 is higher thanthat of the first p-type epitaxial layer 136. In some embodiments, aGroup III-V semiconductor layer is used for at least one of the firstand second p-type epitaxial layers. The combination of the first andsecond p-type epitaxial layers 136 and 138 correspond to thesource/drain epitaxial layer 62. In other embodiments, only one of thefirst and second p-type epitaxial layers 136 and 138 is formed, and incertain embodiments, three or more p-type epitaxial layers are formed.

Further, the alloy layer 220, for example, a silicide layer, whichcorresponds to the alloy layer 81, is formed one the second p-typeepitaxial layer 138. The alloy layer 220 is formed by a reaction betweenthe material of the second p-type epitaxial layer 138 and a transitionmetal layer formed thereon. As shown in FIG. 7, the second p-typeepitaxial layer 138 of one of the adjacent two fin structure 54 does nottouch the second p-type epitaxial layer 138 of the other one of theadjacent two fin structure 54. The alloy layer 220 fills the spacebetween two second p-type epitaxial layers 138 and physically andelectrically connects the two second p-type epitaxial layers 138.

In some embodiments, a residual transition metal 215, which has notfully reacted with the second p-type epitaxial layer 138 remain. In sucha case, the remaining transition metal can be converted to a passivationlayer by a subsequent nitridation operation by using NH₃ or N₂+H₂ plasmain some embodiments. The passivation layer covers the surface of thealloy layer 220 to protect the alloy layer 220 from damages caused bythe subsequent processes. Further, a CESL 150 covers the p-typesource/drain structure, as shown in FIG.7.

The contact plug 201 is in contact with the alloy layer 222. In someembodiments, the contact plug 201 includes a barrier layer 202 made of,for example, TiN or TaN, and a body layer 210 made of, for example, Co,W, Ti, Ta, Cu, Ru, Rh, Jr, Al and/or Ni.

In FIG. 7, a transition metal layer 225 remains at the bottom of thevoid 224 formed by the alloy layer 222 and the isolation insulatinglayer 58. Since the volume of the transition metal layer 225 issufficiently small not to affect electrical properties of the NFET.

Further, in FIG. 7, spacer residues 110, which is a remaining part ofthe sidewall spacers 24 that is not etched in the operation of FIG. 3B,exit.

The width T21 (the largest width) of the fin structure 54 surrounded bythe first p-type epitaxial layer along the X direction is in a rangefrom about 4 nm to about 10 nm in some embodiments. The thickness T22 ofthe first p-type epitaxial layer 136 is in a range from about 0.5 nm toabout 3 nm in some embodiments, and the thickness T23 of the secondp-type epitaxial layer 138 is in a range from about 2 nm to about 8 nmin some embodiments. The space T25 between the two adjacent secondp-type epitaxial layers 138 is in a range from about 0.5 nm to about 20nm in some embodiments.

In some embodiments, one or more voids 144 are formed during the alloylayer formation. The shapes of the voids 144 in the cross section mayinclude a rhombus, a circle, an oval or an irregular shape. The shapesmay be symmetry or asymmetric. The number of the voids may be as smallas one in some embodiments, and more than one in other embodiments.Sizes of the multiple voids and spaces between voids may besubstantially the same or different.

FIG. 8 is an exemplary cross sectional view of source/drain structuresof a FinFET according to another embodiment of the present disclosure.FIG. 8 shows the substantially the same structures as FIG. 7, exceptthere are no spacer residues 110 in this embodiment.

FIG. 9 is an exemplary cross sectional view of source/drain structuresof a FinFET according to another embodiment of the present disclosure.FIG. 9 shows the substantially the same structures as FIG. 7, except forthe shape of the source/drain epitaxial layers. In FIG. 9, the shape ofthe source/drain epitaxial layers (e.g., 132, 134, 136 and 138) has atapered shape having a larger bottom area than an upper area. Dependingon the epitaxial growth conditions, the shapes of the source/drainepitaxial layers may vary.

FIG. 10 is an exemplary cross sectional view of source/drain structuresof a FinFET according to another embodiment of the present disclosure.FIG. 10 shows the substantially the same structures as FIG. 9, exceptthere are no spacer residues 110 in this embodiment.

FIG. 11 is an exemplary cross sectional view of source/drain structuresof a FinFET according to another embodiment of the present disclosure.In FIG. 11, no source/drain epitaxial layers are formed on the finstructures 52. After the structure shown in FIG. 3B is formed, the firstILD 67 is formed without forming the source/drain epitaxial layers 60,62. By performing the same or similar operations as FIGS. 3D-4C, thestructure of FIG. 11 can be obtained.

In FIG. 11, the alloy layers 220 or 222 directly wraps around the finstructure 52 made of a crystalline semiconductor. The spaces T15′ andT25′ between two fin structures covered by the alloy layer 220, 222 isin a range from about 8 nm to about 60 nm in some embodiments.

Although FIG. 11 illustrated the spacer residues 110, in certainembodiments, the spacer residues 110 do not remain.

FIGS. 12-14 are exemplary cross sectional views of source/drainstructures of a FinFET according to the methods shown by FIGS. 5A-6C.The same or similar configurations, structures and/or materials as thoseof FIGS. 7-11 may be employed, and the detailed explanation may beomitted.

After the source/drain epitaxial layers 60 and 62 and the fin structures52 are recessed as shown in FIG. 5B, a first n-type epitaxial layer 131is formed on the recessed fin structure 52, and a second n-typeepitaxial layer 133 is formed on the first n-type epitaxial layer 131for the n-channel FET, and a first p-type epitaxial layer 135 is formedon the recessed fin structure 54, and a second p-type epitaxial layer137 is formed on the first n-type epitaxial layer 135 for the p-channelFET. The combination of the first and second n-type epitaxial layerscorresponds to the source/drain epitaxial layer 113, and the combinationof the first and second p-type epitaxial layers corresponds to thesource/drain epitaxial layer 114.

The first and second n-type epitaxial layers 131, 133 are crystallinesemiconductor layers, such as Si, SiC, SiCP, SiP, Ge and SiGe, havingdifferent lattice constants from each other and from the fin structure.When SiC, SiP and/or SiCP are used, the C or P concentration of thesecond n-type epitaxial layer 131 is higher than that of the firstn-type epitaxial layer 133. In some embodiments, a Group III-Vsemiconductor layer is used for at least one of the first and secondn-type epitaxial layers. In other embodiments, only one of the first andsecond n-type epitaxial layers 131 and 133 is formed, and in certainembodiments, three or more n-type epitaxial layers are formed.

The first and second p-type epitaxial layers 135, 137 are crystallinesemiconductor layers, such as Si, SiC, SiCP, SiP, Ge and SiGe, havingdifferent lattice constants from each other and from the fin structure.When SiGe is used, the Ge concentration of the second p-type epitaxiallayer 137 is higher than that of the first p-type epitaxial layer 135.In some embodiments, a Group III-V semiconductor layer is used for atleast one of the first and second p-type epitaxial layers. In otherembodiments, only one of the first and second p-type epitaxial layers135 and 137 is formed, and in certain embodiments, three or more p-typeepitaxial layers are formed.

Since the first and second n-type and p-type epitaxial layers are formedin the openings 111 and 112 shown in FIG. 5B, the shapes of theepitaxial layers are restricted by the shapes of the openings 111 and112.

The thickness H14 of the first n-type epitaxial layer 131 is in a rangefrom about 0.5 nm to about 3 nm in some embodiments, and the thicknessH15 of the second n-type epitaxial layer 133 is in a range from about 2nm to about 100 nm in some embodiments. The thickness H24 of the firstp-type epitaxial layer 135 is in a range from about 0.5 nm to about 3 nmin some embodiments, and the thickness H25 of the second p-typeepitaxial layer 137 is in a range from about 2 nm to about 100 nm insome embodiments.

FIG. 13 is an exemplary cross sectional view of source/drain structuresof a FinFET according to some embodiments of the present disclosure.FIG. 13 shows the substantially the same structures as FIG. 12, exceptthere are no spacer residues 110 in this embodiment.

FIG. 14 is an exemplary cross sectional view of source/drain structuresof a FinFET according to another embodiment of the present disclosure.

After the structure of FIG. 3A is formed, the fin structures 52 arerecessed to or below the isolation insulating layer 58, and thenepitaxial source/drain structures are formed on the recessed finstructure 52. Subsequently, a cover layer 60 and a first ILD layer 67are formed, and the operations the same as or similar to FIGS. 4A-4C or6A-6C are performed. In this embodiment, since the source/drainepitaxial layers are not formed in the openings, the source/drainepitaxial layers are laterally grown so as to have a diamond crosssectional shape, as shown in FIG. 14.

In more detail, after the fin structures 52 are recessed, a first n-typeepitaxial layer 131 is formed on the recessed fin structure 52, and asecond n-type epitaxial layer 133 is formed on the first n-typeepitaxial layer 131 for the n-channel FET, and a first p-type epitaxiallayer 135 is formed on the recessed fin structure 52, and a secondp-type epitaxial layer 137 is formed on the first n-type epitaxial layer135 for the p-channel FET. The second n-type epitaxial layer 133 has adiamond cross sectional view dues to a lateral growth of the epitaxiallayer, and the second p-type epitaxial layer 137 has a diamond crosssectional view dues to a lateral growth of the epitaxial layer.

The thickness H16 of the first n-type epitaxial layer 131 is in a rangefrom about 0.5 nm to about 3 nm in some embodiments, and the thicknessH17 of the second n-type epitaxial layer 133 is in a range from about 2nm to about 40 nm in some embodiments. The thickness H26 of the firstp-type epitaxial layer 135 is in a range from about 0.5 nm to about 3 nmin some embodiments, and the thickness H27 of the second p-typeepitaxial layer 137 is in a range from about 2 nm to about 40 nm in someembodiments.

FIGS. 15A-18C show exemplary cross sectional views of various stages formanufacturing a FinFET according to another embodiment of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 15A-18C, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. The configurations,structures, materials and/or dimensions same as or similar to thoseexplained with FIGS. 1A-14 may be employed in the following embodimentsand the detailed explanation thereof may be omitted. In the followingembodiments, a gate-all-around FET is employed.

As shown in FIG. 15A, stacked semiconductor layers are formed over thesubstrate 50. The stacked semiconductor layers include firstsemiconductor layers 42 and second semiconductor layers 44. Further, amask layer 10 is formed over the stacked layers.

The first semiconductor layers 42 and the second semiconductor layers 44are made of materials having different lattice constants, and mayinclude one or more layers of Si, Ge, SiGe, GaAs, InSb, GaP, GaSb,InAlAs, InGaAs, GaSbP, GaAsSb or InP. In some embodiments, the firstsemiconductor layers 42 and the second semiconductor layers 44 are madeof Si, a Si compound, SiGe, Ge or a Ge compound. In an embodiment, thefirst semiconductor layers 42 are Si_(1-x)Ge_(x), where x is more thanabout 0.3, or Ge (x=1.0) and the second semiconductor layers 44 are Sior Si_(1-y)Ge_(y), where y is less than about 0.4, and x>y. In thisdisclosure, an “M” compound” or an “M based compound” means the majorityof the compound is M.

In another embodiment, the second semiconductor layers 44 areSi_(1-y)Ge_(y), where y is more than about 0.3, or Ge, and the firstsemiconductor layers 42 are Si or Si_(1-x)Ge_(x), where x is less thanabout 0.4, and x<y. In yet other embodiments, the first semiconductorlayer 42 is made of Si_(1-x)Ge_(x), where x is in a range from about 0.3to about 0.8, and the second semiconductor layer 44 is made ofSi_(1-x)Ge_(x), where x is in a range from about 0.1 to about 0.4.

In FIG. 15A, four layers of the first semiconductor layer 42 and fourlayers of the second semiconductor layer 44 are disposed. However, thenumber of the layers are not limited to four, and may be as small as 1(each layer) and in some embodiments, 2-10 layers of each of the firstand second semiconductor layers are formed. By adjusting the numbers ofthe stacked layers, a driving current of the GAA FET device can beadjusted.

The first semiconductor layers 42 and the second semiconductor layers 44are epitaxially formed over the substrate 50. The thickness of the firstsemiconductor layers 42 may be equal to or greater than that of thesecond semiconductor layers 44, and is in a range from about 5 nm toabout 50 nm in some embodiments, and is in a range from about 10 nm toabout 30 nm in other embodiments. The thickness of the secondsemiconductor layers 44 is in a range from about 5 nm to about 30 nm insome embodiments, and is in a range from about 10 nm to about 20 nm inother embodiments. The thickness of each of the first semiconductorlayers 42 may be the same, or may vary.

In some embodiments, the mask layer 10 includes, for example, a padoxide (e.g., silicon oxide) layer 11 and a silicon nitride mask layer12, as shown in FIG. 15A.

A mask pattern is further formed over the mask layer. The mask patternis, for example, a resist pattern formed by lithography operations. Byusing the mask pattern as an etching mask, a hard mask pattern of thepad oxide layer 11 and the silicon nitride mask layer 12 is formed, asshown in FIG. 15B.

Then, as shown in FIG. 15C, by using the hard mask pattern as an etchingmask, the stacked semiconductor layer 42, 44 and the substrate 50 arepatterned into fin structures 152 for an n-type FET and fin structures154 for a p-type FET by trench etching using a dry etching method and/ora wet etching method. The dimensions for the fin structures 152 for ann-type FET may be the same as or different from those for the finstructures 154 for a p-type FET.

After the fin structures 152, 154 are formed, similar to FIG. 1D, afirst protective layer 15 is formed to cover the structures 152, 154, asshown in FIG. 15D.

After the first protective layer 15 is formed, similar to FIG. 2A, asecond protective layer 17 is formed as shown in FIG. 16A.

Further, similar to FIG. 2B, an isolation insulating layer (STI) 58 isformed in spaces between the fin structures and/or a space between onefin structure and another element formed over the substrate 50, as shownin FIG. 16B.

Similar to FIGS. 2B and 2C, the thick insulating layer 58 is recessed soas to expose the upper portions of the fin structures 152, 154, as shownin FIG. 16C. The height H2′ of the fin structures from the upper surfaceof the isolation insulating layer 58 is in a range from about 20 nm toabout 100 nm in some embodiments, and is in a range from about 30 nm toabout 50 nm in other embodiments.

Similar to FIG. 2D, after the insulating layer 58 is formed (andrecessed), a dummy gate structure including a dummy gate dielectriclayer 20 and a dummy gate electrode layer 22 is formed over the finstructures 152, 154, as shown in FIG. 16D.

Further, similar to FIG. 3C, sidewall spacers 24 are formed on oppositesidewalls of the dummy gate electrode layer 22, as shown in FIG. 17A.

Then, as shown in FIG. 17B, the sidewall spacers 24 formed on the finstructures 152, 154 are removed by using, for example, anisotropic dryetching, so as to expose source/drain regions (stacked semiconductorlayer portion) of the structures 152, 154. After the source/drainregions are exposed, the first semiconductor layers 42 are selectivelyremoved by using a wet etchant such as, but not limited to, ammoniumhydroxide (NH₄OH), tetramethylammonium hydroxide (TMAH), ethylenediaminepyrocatechol (EDP), or potassium hydroxide (KOH) solution. In otherembodiments, the second semiconductor layers 44 are selectively removed.In certain embodiments, the first semiconductor layer 42 are removed forn-channel FETs and the second semiconductor layers 44 are removed forp-channel FETs. Yet in other embodiments, the second semiconductor layer44 are removed for n-channel FETs and the first semiconductor layers 42are removed for p-channel FETs.

Subsequently, source/drain epitaxial layers 46, 48 are formed, as shownin FIG. 17C. The source/drain epitaxial layer 46 for the n-type FETincludes one or more layers of semiconductor material, such as, SiC, SiPand SiCP, which provides appropriate stress to the channel of the n-typeFET, in some embodiments. Since the second semiconductor layers 44 are acrystalline semiconductor, the epitaxial layer 46 is also crystalline.The source/drain epitaxial layer 48 for the p-type FET includes one ormore of semiconductor material, such as, Ge and Si_(x)Ge_(1-x) where0<x<1, which provides appropriate stress to the channel of the p-typeFET, in some embodiments. Since the second semiconductor layers 44 are acrystalline semiconductor, the epitaxial layer 48 is also crystalline.

The source/drain epitaxial layers 46, 46 may be selectively grown on andaround the second semiconductor layers 44 at a temperature of about 600to 800° C. under a pressure of about 80 to 150 Torr, by using a Sicontaining gas such as SiH₄, Si₂H₆ or SiCl₂H₂; a Ge containing gas, suchas GeH₄, Ge₂H₆ or GeCl₂H₂; a C containing gas, such as CH₄ or C₂H₆;and/or a dopant gas, such as PH₃. The source/drain structure for ann-type FET and the source/drain structure for a p-type FET may be formedby separate epitaxial processes.

After the source/drain epitaxial layers 46 and 48 are formed, adielectric cover layer 45 is formed over the source/drain epitaxiallayers 46 and 48 and a first interlayer dielectric (ILD) layer 67 isformed over the dielectric cover layer 45, as shown in FIG. 17D. Thedielectric cover layer 55 is made of, for example, SiN or SiON, and hasa thickness in a range from about 2 nm to about 20 nm in someembodiments. The first ILD 67 is made of a different material than thedielectric cover layer 45 and is made of, for example, one or morelayers of silicon oxide, SiCN, SiOCN or a low-k material.

After the first ILD layer 67 is formed, a nano-wire channel structureand a metal gate structure are formed. In certain embodiments, the firstILD layer 67 is formed over the dummy gate structures and aplanarization operation, such as a chemical mechanical polishing (CMP)process or an etch-back process, is performed to expose the uppersurface of the dummy gate electrode layer 22. The dummy gate structures(the dummy gate electrode layer 22 and the dummy gate dielectric layer20) are removed by using suitable etching operations, so as to exposestacked structures of the first semiconductor layers 42 and the secondsemiconductor layers 44. Then, the first semiconductor layers 42 areelectively removed, so as to leave the second semiconductor layers 44 asnano-wire channels. A metal gate structure including a gate dielectriclayer 72 and a metal gate electrode layer 74 are formed so as to wraparound the second semiconductor layers 44, as shown in FIG. 18A. One ormore layers of work function adjustment metal may be formed between thegate dielectric layer 72 and the metal gate electrode layer 74.

In other embodiments, the second semiconductor layers 44 are selectivelyremoved, so as to leave the first semiconductor layers 42 as nano-wirechannels. In certain embodiments, the first semiconductor layer 42 areremoved for n-channel FETs and the second semiconductor layers 44 areremoved for p-channel FETs. Yet in other embodiments, the secondsemiconductor layer 44 are removed for n-channel FETs and the firstsemiconductor layers 42 are removed for p-channel FETs.

After the metal gate structure is formed, the first ILD layer 67 anddielectric cover layer 45 are removed. In an embodiment, the first ILDlayer 67 and dielectric cover layer 45 are fully removed and in otherembodiments, the first ILD layer 67 and dielectric cover layer 45 arepartially removed from an area around the source/drain structures.

After the first ILD layer 67 is at least partially removed, similar toFIG. 4B, a metal alloy layer 80, 81 is formed over the source/drainepitaxial layer 46 and 48, as shown in FIG. 18B. The alloy layer 80 isone or more of TiSi, TaSi, NiSi, CoSi, TiSiGe, TaSiGe, NiSiGe andCoSiGe.

After the first ILD layer 67 is removed, transition metal is depositedby, for example, CVD, ALD or PVD, on the source/drain epitaxial layer 46and 48. During the deposition, the deposited transition metal reactswith Si and/or Ge in the source/drain epitaxial layer 46 and 48, therebyforming the alloy layer 80, 81 in some embodiments.

In the present embodiments, before the alloy layer 80, 81 is formed, thesource/drain epitaxial layer 46 formed on one of the secondsemiconductor layers 44 is separated from the source/drain epitaxiallayer 46 formed on the adjacent one of the second semiconductor layers44 of the first fin structure, and the source/drain epitaxial layer 48formed on one of the second semiconductor layers 44 is separated fromthe source/drain epitaxial layer 48 formed on the adjacent one of thesecond semiconductor layers 44 of the second fin structure. The alloylayer 80, 81 is formed such that the formed alloy layer 80 connects thesource/drain epitaxial layer 46 of one of the second semiconductorlayers 44 and the source/drain epitaxial layer 46 of the adjacent one ofthe second semiconductor layers 44, and the alloy layer 81 connects thesource/drain epitaxial layer 48 of one of the second semiconductorlayers 44 and the source/drain epitaxial layer 62 of the adjacent one ofthe second semiconductor layers 44.

In some embodiments, after a transition metal layer is formed on thesource/drain epitaxial layer 46 and 48, an annealing operation isperformed to form the alloy layer 80, 81. The annealing operation isperformed at a temperature of about 250° C. to about 850° C.

After the alloy layer 80, 81 is formed, similar to FIG. 4C, acontact-etch stop layer (CESL) 150 is formed to cover the alloy layer80, 81, and a second ILD layer 160 is formed on the CESL 150, as shownin FIG. 18C. Subsequently, similar to FIG. 4C, a patterning operation isperformed to form contact openings over the alloy layer 80, 81 of thesource/drain structure, and the openings are filled with a conductivematerial, thereby forming contact plugs 200 and 201, as shown in FIG.18C.

After forming the contact plugs, further CMOS processes are performed toform various features such as additional interlayer dielectric layer,contacts/vias, interconnect metal layers, and passivation layers, etc.

In certain embodiments, the operations as explained with FIGS. 5A-6C areemployed for a gate-all-around field effect transistor (GAA FET) asexplained above.

FIG. 19 is an exemplary cross sectional view (X-cut) of source/drainstructures of a GAA FET according to some embodiments of the presentdisclosure. In FIG. 19, an n-channel GAA FET (NFET) and a p-channel GAAFET (PFET) are illustrated as adjacent to each other. However, theconfiguration is not limited to this. The number of the fin structuresmay be two or more and one or more additional structures may be disposedbetween the NFET and the PFET.

In FIG. 19, in the n-channel GAA FET (NFET), n-type semiconductor wirelayers 332 (corresponding to, e.g., the second semiconductor layers 44)are disposed over the fin structure 152, and an n-type epitaxial layers334 (corresponding to, e.g., the source/drain epitaxial layers 46) areformed to wrap around the n-type semiconductor wire layers 332. Then-type semiconductor wire layers 332 and the n-type epitaxial layers 334are crystalline semiconductor layers, such as Si, SiC, SiCP, SiP, Ge andSiGe, having different lattice constants from each other and from thefin structure. When SiC, SiP and/or SiCP are used, the C or Pconcentration of the n-type epitaxial layer 334 is higher than that ofthe n-type semiconductor wire layers 332. In some embodiments, a GroupIII-V semiconductor layer is used for at least one of the semiconductorwire layers and the n-type epitaxial layers. In certain embodiments, twoor more n-type epitaxial layers are formed. Further, the number ofn-type semiconductor wire layers 332 is not limited.

Further, the alloy layer 322, for example, a silicide layer, whichcorresponds to the alloy layer 80, is formed around the n-type epitaxiallayer 334. As shown in FIG. 19, one n-type epitaxial layer 334 does nottouch the adjacent n-type epitaxial layer 334. The alloy layer 322 fillsthe space between two n-type epitaxial layers 334 and physically andelectrically connects the two n-type epitaxial layers 334.

In some embodiments, a residual transition metal 324, which has notfully reacted with the n-type epitaxial layer 334, remains. In such acase, the remaining transition metal can be converted to a passivationlayer by a subsequent nitridation operation by using NH₃ or N₂+H₂ plasmain some embodiments. The passivation layer covers the surface of thealloy layer 322 to protect the alloy layer 322 from damages caused bythe subsequent processes. The contact plug 200 is in contact with thealloy layer 322. In some embodiments, the contact plug 200 includes abarrier layer 202 made of, for example, TiN or TaN, and a body layer 210made of, for example, Co, W, Ti, Ta, Cu, Ru, Rh, Jr, Al and/or Ni. Insome embodiments, spacer residues, which are a remaining part of thesidewall spacers 24 that is not etched in the operation of FIG. 17B,exist.

The thickness T84 of the n-type semiconductor wire layers 332 is in arange from about 5 nm to about 50 nm in some embodiments, and is in arange from about 10 nm to about 30 nm in other embodiments. The spaceT85 between two adjacent n-type semiconductor wire layers 332 is in arange from about 5 nm to about 50 nm in some embodiments, and is in arange from about 10 nm to about 30 nm in other embodiments. Thethickness T86 of the n-type epitaxial layers 334 is in a range fromabout 1 nm to about 30 nm in some embodiments, and is in a range fromabout 2 nm to about 7 nm in other embodiments. The space T87 betweenadjacent n-type epitaxial layers 334 is in a range from about 1 nm toabout 10 nm in some embodiments, and is in a range from about 2 nm toabout 5 nm in other embodiments.

The p-channel GAA FET (PFET) shown in FIG. 19 has the same or similarstructure as the n-channel FET (NFET), and explanations for the commonconfigurations may be omitted. P-type semiconductor wire layers 336(corresponding to, e.g., the second semiconductor layers 44) aredisposed over the fin structure 154, and p-type epitaxial layers 338(corresponding to, e.g., the source/drain epitaxial layers 48) areformed to wrap around the p-type semiconductor wire layers 336. Thesemiconductor wire layers and the p-type epitaxial layers arecrystalline semiconductor layers, such as Si, SiC, SiCP, SiP, Ge andSiGe, having different lattice constants from each other and from thefin structure. When SiGe is used, the Ge concentration of the secondp-type epitaxial layer 338 is higher than that of the semiconductor wirelayers 336. In other embodiments, two or more p-type epitaxial layersare formed. Further, the number of p-type semiconductor wire layers 336is not limited.

Further, the alloy layer 320, for example, a silicide layer, whichcorresponds to the alloy layer 81, is formed to wrap around the p-typeepitaxial layers 338. As shown in FIG. 19, the p-type epitaxial layer338 formed on one of the adjacent two semiconductor wires 336 does nottouch the p-type epitaxial layer 338 of the other one of the adjacenttwo semiconductor wires 336. The alloy layer 320 fills the space betweentwo p-type epitaxial layers 338 and physically and electrically connectsthe two p-type epitaxial layers 338.

The thickness T94 of the p-type semiconductor wire layers 336 is in arange from about 5 nm to about 50 nm in some embodiments, and is in arange from about 10 nm to about 30 nm in other embodiments. The spaceT95 between two adjacent p-type semiconductor wire layers 336 is in arange from about 5 nm to about 50 nm in some embodiments, and is in arange from about 10 nm to about 30 nm in other embodiments. Thethickness T96 of the p-type epitaxial layers 338 is in a range fromabout 1 nm to about 30 nm in some embodiments, and is in a range fromabout 2 nm to about 7 nm in other embodiments. The space T97 betweenadjacent p-type epitaxial layers 338 is in a range from about 1 nm toabout 10 nm in some embodiments, and is in a range from about 2 nm toabout 5 nm in other embodiments.

FIG. 20 illustrates exemplary cross sectional views (Y-cut) ofsource/drain structures of a gate-all-around field effect transistor(GAA FET) according to another embodiment of the present disclosure. (B)and (C) of FIG. 20 correspond to the area Al of (A) of FIG. 20. In thisembodiment, the n-type semiconductor wire layers 332 and p-typesemiconductor wire layers 336 are epitaxially formed layers differentfrom the second semiconductor layers 44. For example, the first andsecond semiconductor layers 42, 44 are fully removed from thesource/drain region at the operation of FIG. 17B, and the n-typesemiconductor wire layers 332 and p-type semiconductor wire layers 336are epitaxially formed on the second semiconductor layers 44 extendingfrom the channel region. The n-type semiconductor wire layers 332 andp-type semiconductor wire layers 336 penetrate under the spacer layers82 in an amount T70 or T72 of about 2 nm to about 10 nm in someembodiments.

FIGS. 21A and 21B are exemplary cross sectional views (Y-cut) ofsource/drain structures of a gate-all-around field effect transistor(GAA FET) according to another embodiment of the present disclosure.Similar to FIG. 20, the n-type semiconductor wire layers 332 and p-typesemiconductor wire layers 336 are epitaxially formed layers differentfrom the second semiconductor layers 44. Unlike FIG. 20, the n-typesemiconductor wire layers 332 of one GAA FET are separated from that ofadjacent GAA FET, and connected by the n-type epitaxial layers 334.Similarly, the p-type semiconductor wire layers 336 of one GAA FET areseparated from that of adjacent GAA FET, and connected by the p-typeepitaxial layers 338. In this embodiment, the n-type epitaxial layers334 are physically separated from each other and are connected by thealloy layer 322, and the p-type epitaxial layers 338 are physicallyseparated from each other and are connected by the alloy layer 320.

In FIG. 21A, the n-type epitaxial layers 334 and the p-type epitaxiallayers 338 have the maximum thickness at the middle potion thereof, andin FIG. 21B, the p-type epitaxial layers 338 have the minimum thicknessat the middle portion thereof. The maximum thickness is in a range fromabout 10 nm to about 40 nm and the minimum thickness is in a range fromabout 0.5 nm to about 5 nm, in some embodiments. The angle TH formed bythe n-type or p-type epitaxial layers and the sidewall spacers 84 is ina range from about 30° to 60° in some embodiments. In the structureshown in FIG. 21A, it is possible to increase a contact area. In thestructure shown in FIG. 21B, it is possible to provide a larger tensilestress to the channel due to a larger silicide volume.

In the present disclosure, source/drain epitaxial layers are separatedbut connected by an alloy layer (e.g., silicide layer) and the alloylayer wraps around the epitaxial layers, respectively. With thisstructure, it is possible to minimize variation of device performancedue to misalignment between contact plugs and the source/drainstructures.

When two epitaxial layers grown over two adjacent fin structures mergesand then metal silicide layer is formed over the merged epitaxiallayers, after contact holes for the plugs are formed, metal or metalsilicide is formed only within the contact hole and atop the merged S/Depitaxial layers. The total contact area between the metal silicide andepitaxial structure is severely limited or is small. This means that thecontact resistance to the source-drain region would be high. Inaddition, the epitaxially grown source/drain structure conducts currentand enables the spreading of the current throughout the fins. However,an epitaxially grown source/drain is not as conductive as a metallicmaterial. When the epitaxial layers are not merged but the space betweenthem is filled with an insulating material, similar problems as setforth above would occur.

In contrast, in the present embodiments, the space between adjacent twosource/drain epitaxial layers is fully filled with the metal silicide.Accordingly, it is possible to maximize the total metalsilicide/epitaxial layer interfacial contact area via the wrap aroundsilicide scheme so as to reduce overall contact resistance fortransistors; and to obtain improved processing margin and improvedtolerances for several key manufacturing variations.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with one aspect of the present disclosure, a semiconductordevice includes a field effect transistor (FET). The FET includes afirst channel, a first source and a first drain; a second channel, asecond source and a second drain; and a gate structure disposed over thefirst and second channels. The gate structure includes a gate dielectriclayer and a gate electrode layer. The first source includes a firstcrystal semiconductor layer and the second source includes a secondcrystal semiconductor layer. The first source and the second source areconnected by an alloy layer made of one or more Group IV element and oneor more transition metal elements. The first crystal semiconductor layeris not in direct contact with the second crystal semiconductor layer.

In accordance with another aspect of the present disclosure, asemiconductor device including a fin field effect transistor (Fin FET).The Fin FET includes a substrate; an insulating layer formed on thesubstrate; a first fin protruding from the substrate, an upper part ofthe first fin projecting from the insulating layer as a first channel; afirst source and a first drain contacting the first channel; a secondfin protruding from the substrate, an upper part of the second finprojecting from the insulating layer as a second channel; a secondsource and a second drain contacting the second channel; and a gatestructure disposed over the first and second channels, the gatestructure including a gate dielectric layer and a gate electrode layer.The first source includes a first crystal semiconductor layer made of adifferent material than the first channel. The second source includes asecond crystal semiconductor layer made of a different material than thesecond channel. The first source and the second source are connected bya metal alloy layer. The metal alloy layer is formed by a reactionbetween a metal and the first source and the second source. The firstcrystal semiconductor layer is not in direct contact with the secondcrystal semiconductor layer.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device including a field effecttransistor (FET), a first FET structure having a first channel, a firstsource, a first drain and a common gate, and a second FET structurehaving a second channel, a second source, a second drain and the commongate are formed. An alloy layer is formed on the first and secondsources. The first source includes a first crystal semiconductor layerand the second source includes a second crystal semiconductor layer. Thefirst source and the second source are connected by the alloy layer. Thealloy layer is made of one or more Group IV element and one or moretransition metal elements. The first crystal semiconductor layer is notin direct contact with the second crystal semiconductor layer.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device including a field effecttransistor (FET), the FET comprising: a first semiconductor wire havinga first channel, a first source and a first drain; a secondsemiconductor wire having a second channel, a second source and a seconddrain; and a gate structure disposed over the first and second channels,the gate structure including a gate dielectric layer and a gateelectrode layer, wherein: the first semiconductor wire and the secondsemiconductor wire are vertically arranged over a bottom fin structuresuch that the first semiconductor wire is disposed between the secondsemiconductor wire and the bottom fin structure in a vertical direction,the FET includes a first crystal semiconductor layer wrapping around thefirst source and a second crystal semiconductor layer wrapping aroundthe second source, the first source and the second source are in contactwith and connected by an alloy layer, the first crystal semiconductorlayer is not in direct contact with the second crystal semiconductorlayer, and the alloy layer fully covers the first and second crystalsemiconductor layers.
 2. The semiconductor device of claim 1, wherein aspace between the first crystal semiconductor layer and the secondcrystal semiconductor layer is filled with the alloy layer.
 3. Thesemiconductor device of claim 1, wherein the first crystal semiconductorlayer is a multi-layer of different crystal semiconductor materials. 4.The semiconductor device of claim 1, wherein the alloy layer directlycovers the first crystal semiconductor layer.
 5. The semiconductordevice of claim 1, wherein the channel is made of Si, Si_(x)Ge_(1-x)where 0<x<1 or Ge.
 6. The semiconductor device of claim 5, wherein thefirst crystal semiconductor layer includes at least one of Si, SiC, SiP,SiCP, Si_(x)Ge_(1-x) where 0<x<1 and Ge.
 7. The semiconductor device ofclaim 6, wherein the alloy layer is one or more of TiSi, TaSi, NiSi,CoSi, TiSiGe, TaSiGe, NiSiGe and CoSiGe.
 8. The semiconductor device ofclaim 7, wherein: a metal layer is disposed on the alloy layer, and themetal layer is made of one or more of Ti, Ta, Ni and Co.
 9. Thesemiconductor device of claim 1, wherein the FET further comprises asource contact plug in contact with the alloy layer.
 10. A semiconductordevice including a fin field effect transistor (Fin FET), the Fin FETcomprising: a substrate; an insulating layer formed on the substrate; abottom fin embedded in the insulating layer; a plurality ofsemiconductor wires disposed and arranged over the bottom fin, each ofthe plurality of semiconductor wires having a channel region, a sourceregion and a drain region; a gate structure disposed over the channelregion, the gate structure including a gate dielectric layer and a gateelectrode layer; a source epitaxial semiconductor layer made of adifferent material than the source region and wrapping around the sourceregion; and a metal alloy layer wrapping around the source epitaxiallayer, wherein the source epitaxial layer is not in direct contact withadjacent source epitaxial layers.
 11. The semiconductor device of claim10, wherein a space between adjacent source epitaxial layers is filledwith the metal alloy layer.
 12. The semiconductor device of claim 10,wherein the source epitaxial layer includes multi layers of differentcrystal semiconductor materials.
 13. The semiconductor device of claim10, wherein the metal alloy layer directly covers the source epitaxiallayer.
 14. The semiconductor device of claim 10, wherein: each of thesemiconductor wires is made of Si, Si_(x)Ge_(1-x) where 0<x<1 or Ge, thesource epitaxial layer includes at least one of Si, SiC, SiP, SiCP,Si_(x)Ge_(1-x) where 0<x <1 and Ge.
 15. The semiconductor device ofclaim 10, wherein the metal alloy layer is one or more of TiSi, TaSi,NiSi, CoSi, TiSiGe, TaSiGe, NiSiGe and CoSiGe.
 16. A semiconductordevice, comprising: a first semiconductor wire having a first channelregion and a first source region; a second semiconductor wire having asecond channel and a second source region; a first gate structuredisposed over the first channel region; a second gate structure disposedover the second channel region; a first source epitaxial layer formedover the first source region and the second source region and laterallyconnecting the first source region and the second source region; and ametal alloy layer wrapping around the first source epitaxial layer,wherein the first source region is not in direct contact with the secondsource region.
 17. The semiconductor device of claim 16, furthercomprising: a third semiconductor wire having a third channel region anda third source region and disposed above the first semiconductor wire; afourth semiconductor wire having a fourth channel and a fourth sourceregion and disposed above the second semiconductor wire, wherein: thefirst gate structure is disposed over the third channel region, thesecond gate structure is disposed over the fourth channel region, asecond source epitaxial layer is formed over the third source region andthe fourth source region and laterally connecting the third sourceregion and the fourth source region; and the metal alloy layer wrappingaround the second source epitaxial layer.
 18. The semiconductor deviceof claim 17, wherein the first to fourth semiconductor wires include atleast one of Si, SiC, SiP, SiCP, Si_(x)Ge_(1-x) where 0<x<1 and Ge. 19.The semiconductor device of claim 17, wherein the metal alloy layer isone or more of TiSi, TaSi, NiSi, CoSi, TiSiGe, TaSiGe, NiSiGe andCoSiGe.
 20. The semiconductor device of claim 17, wherein: a metal layeris disposed on the metal alloy layer, and the metal layer is made of oneor more of Ti, Ta, Ni and Co.